US4816703A - On-line serial communication interface from a current loop to a computer and/or terminal - Google Patents
On-line serial communication interface from a current loop to a computer and/or terminal Download PDFInfo
- Publication number
- US4816703A US4816703A US06/764,914 US76491485A US4816703A US 4816703 A US4816703 A US 4816703A US 76491485 A US76491485 A US 76491485A US 4816703 A US4816703 A US 4816703A
- Authority
- US
- United States
- Prior art keywords
- transmitter
- current
- current loop
- comparator
- pulses
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
-
- G—PHYSICS
- G08—SIGNALLING
- G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
- G08C19/00—Electric signal transmission systems
- G08C19/02—Electric signal transmission systems in which the signal transmitted is magnitude of current or voltage
Definitions
- the present invention relates in general to digital interface equipment, and in particular to a new and useful on-line serial communication interface from a transmitter of a current loop to a computer or hand-held terminal.
- Two-wire analog transmission systems are well known. Such systems include a transmitter which is connected to a power supply by two wires which from a current loop.
- the transmitter includes, as at least one of its features, a transducer which senses a condition such as pressure or temperature. This condition is known as a process variable (PV).
- PV process variable
- a power supply is connected to the two wires to close the current loop. It is also conventional to provide a resistor in the current loop.
- the transmitter amplifies the signal from its transducer and this amplified signal is used to draw a certain current from the power supply which is proportional or otherwise related to the process variable. It is conventional to draw from a minimum of 4 mA to a maximum of 20 mA.
- the current between 4 and 20 mA passes through the resistor to produce a voltage drop across the resistor. This voltage drop can be measured to give a value for the process variable.
- the 4 mA minimum current is required to energize the circuitry of the transmitter. Any excess current above this 4 mA level is taken as a value which can be used to determine the process variable.
- the transmitters in such circuits are generally limited in accuracy to about 0.1% and their functionality is limited to only continuous reading and sensing of the process variable.
- the present invention utilizes microprocessor technology to improve the overall accuracy and expand the functionality of transmitter devices.
- the present invention provides an apparatus for interfacing a computer or hand-held terminal with a current loop for communication from a two-wire analog current loop transmitter which the transmitter is still on-line (sending analog information) to a controller or some other monitoring device.
- an object of the present invention is to provide an on-line serial communication interface for a digital circuit such as a computer or hand-held terminal, which digital circuit receives voltages pulses, representing distinct values of the process variable from a current loop having lines for connecting a transmitter to a power supply for drawing current from the power supply according to a process variable sensed by the transmitter and for modulating the current on the current loop, comprising a resistor connected in series in one of the lines of the current loop for establishing a voltage drop on the one line which depends on current drawn by the transmitter, a capacitor connected to the one line for receiving the voltage drop on the one line, the voltage drop being modulated into voltage pulses when the transmitter modulates the current on the one line, and a comparator having an output connected to the digital circuit, and having two inputs, one of the inputs being connected to the capacitor for receiving the voltage pulses and the outer input being connected to a selected constant voltage whereby the comparator outputs voltage pulses which are applied to the digital circuit.
- a further object of the invention is to provide a serial communication interface between a current loop and a digital circuit which is simple in design, rugged in construction and economical to manufacture.
- FIG. 1 is a block diagram showing a conventional current loop having a communication device such as a computer or hand-held terminal connected to the current loop; and
- FIG. 2 is a schematic diagram of the inventive on-line serial communication interface between the communication device and the current loop.
- the present invention provides an on-line serial communication interface 22 between a digital circuit shown as communication device 24 in FIG. 1, such as; and IBM PC, Radio Shack Model 100 or, Termiflex hand held Terminal, and a current loop formed by Bailey's Smart transmitter 10, lines 12,14 and any 12-48 DC volt power supply 16.
- a digital circuit shown as communication device 24 in FIG. 1 such as; and IBM PC, Radio Shack Model 100 or, Termiflex hand held Terminal, and a current loop formed by Bailey's Smart transmitter 10, lines 12,14 and any 12-48 DC volt power supply 16.
- one of the lines 14 may include a resistor RO, which has a voltage drop thereacross proportional to a current flowing in the lines 12,14.
- Transmitter 10 may include a transducer such as a pressure or temperature transducer (not shown) which receives a process variable PV. The transducer may be connected to a microprocessor in transmitter 10 which controls the amount of the current to be drawn from power supply 16 on lines 12 and 14.
- the voltage drop across resistor RO is measure by an analog-to-digital convertor 18. This voltage drop can be displayed on a display unit 20 as a measurement of the process variable PV.
- a Serial Interface 22 is connected to current loop line 14 by connecting lines 26 and 28.
- Communicating device 24 is connected to the serial interface 22 through line 30.
- Communicating device 24 is a digital circuit such as a computer, microprocessor, or hand-held terminal.
- Device 24 receives digital information in the form of voltage pulses on line 30 for establishing digital communication with the current loop.
- Device 24 includes an RS-232C device which receives and/or sends a digital signal one bit at a time. A logic high is between +3 and +12 volts, a logic low is between -3 and -12 volts.
- FIG. 2 illustrates the on-line serial communication interface of the present invention.
- the transmitter pulses the current on line 14.
- the current pulses produce corresponding voltage pulses which appear at a line 28 connected to line 14.
- a capacitor C1 is connected to line 28 for receiving the voltage pulses and transmitting them to the positive terminal of a comparator or differential amplifier 32.
- the output of amplifier 32 is connected to the communicating device 24, for example over line 30.
- the communicating device is in the form of a computer or hand-held terminal and is structured to receive and process large voltage pulses for RS-232C communication.
- comparator 32 The negative terminal of comparator 32 is held slightly positive by a resistor divider circuit made up of resistors R2 and R3. This divider circuit is connected to a source of constant voltage V+. This keeps any noise across resistor R1 from tripping the comparator 32. It also holds the output of the comparator at line 30, at ground potential which is necessary for idle operation of RS-232C device 24.
- the comparator converts the 80 mV pulses into large voltage pulses needed for communication with the digital circuit 24.
- Point 34 is also connected to ground over resistor R4 for the proper functioning of comparator 32.
- a major advantage of the present invention is that communication can be achieved while the transmitter is still on-line with a controller. This is possible because there is little effect on the current in the loop. Communication is down by modulating the current in the loop by a small amount. That is the current modulation is small with respect to the 4-20 mA current needed for analog communication from the transmitter 10.
- Another advantage is that the interface is powered by using the requestto-send line from the RS-232C port of the operator's communicating device 24. No extra power supply is necessary.
Abstract
Description
Claims (4)
Priority Applications (10)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/764,914 US4816703A (en) | 1985-08-12 | 1985-08-12 | On-line serial communication interface from a current loop to a computer and/or terminal |
IN341/CAL/86A IN165456B (en) | 1985-08-12 | 1986-04-30 | |
KR1019860004060A KR870002507A (en) | 1985-08-12 | 1986-05-23 | Online serial communication interface |
CA000510378A CA1243095A (en) | 1985-08-12 | 1986-05-30 | On-line serial communication interface from a current loop to a computer and/or terminal |
ES556791A ES8800458A1 (en) | 1985-08-12 | 1986-06-25 | On-line serial communication interfaces. |
AU59421/86A AU585032B2 (en) | 1985-08-12 | 1986-06-27 | On line serial communication interface from a current loop to a computer and/or terminal |
BR8603294A BR8603294A (en) | 1985-08-12 | 1986-07-14 | ONLINE SERIAL COMMUNICATION INTERFACE AND METHOD FOR ESTABLISHING CURRENT CIRCUIT TERMINAL LINE COMMUNICATION |
DE8686305965T DE3679119D1 (en) | 1985-08-12 | 1986-08-01 | ON-LINE SERIAL TRANSFER INTERFACES. |
EP86305965A EP0212897B1 (en) | 1985-08-12 | 1986-08-01 | On-line serial communication interfaces |
JP61184359A JPS6239925A (en) | 1985-08-12 | 1986-08-07 | Online type serial communication interface to computer and/or terminal from current loop |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/764,914 US4816703A (en) | 1985-08-12 | 1985-08-12 | On-line serial communication interface from a current loop to a computer and/or terminal |
Publications (1)
Publication Number | Publication Date |
---|---|
US4816703A true US4816703A (en) | 1989-03-28 |
Family
ID=25072152
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US06/764,914 Expired - Fee Related US4816703A (en) | 1985-08-12 | 1985-08-12 | On-line serial communication interface from a current loop to a computer and/or terminal |
Country Status (10)
Country | Link |
---|---|
US (1) | US4816703A (en) |
EP (1) | EP0212897B1 (en) |
JP (1) | JPS6239925A (en) |
KR (1) | KR870002507A (en) |
AU (1) | AU585032B2 (en) |
BR (1) | BR8603294A (en) |
CA (1) | CA1243095A (en) |
DE (1) | DE3679119D1 (en) |
ES (1) | ES8800458A1 (en) |
IN (1) | IN165456B (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5451923A (en) * | 1992-10-05 | 1995-09-19 | Fisher Controls International, Inc. | Communication system and method |
US5694109A (en) * | 1996-09-04 | 1997-12-02 | International Controls And Measurement Corp. | Two-wire dc communication system and transceiver |
US20030053547A1 (en) * | 2001-08-22 | 2003-03-20 | Peter Aberl | Serial interface unit with transmit monitor |
US9812825B2 (en) | 1998-04-10 | 2017-11-07 | Chrimar Systems, Inc. | Ethernet device |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4604566A (en) * | 1985-08-07 | 1986-08-05 | The Babcock & Wilcox Company | Voltage pulse to current regulating convertor |
JP2580343B2 (en) * | 1989-10-13 | 1997-02-12 | 株式会社日立製作所 | Field instrument system and communicator |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4166963A (en) * | 1976-09-30 | 1979-09-04 | The Solartron Electronic Group Limited | Buffer circuit for a data highway |
US4623799A (en) * | 1985-03-27 | 1986-11-18 | Trw Inc. | High speed analog/digital driver |
US4691328A (en) * | 1985-08-12 | 1987-09-01 | The Babcock & Wilcox Company | On-line serial communication interface from a computer to a current loop |
US4729125A (en) * | 1985-08-12 | 1988-03-01 | The Babcock & Wilcox Company | On-line serial communication interface to a transmitter from a current loop |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4520488A (en) * | 1981-03-02 | 1985-05-28 | Honeywell, Inc. | Communication system and method |
CA1173927A (en) * | 1981-11-02 | 1984-09-04 | Felix J. Houvig | Communication system and method |
DE3280015D1 (en) * | 1982-08-19 | 1989-12-14 | Honeywell Inc | Improvements in 2-wire analog communication systems |
JPS59201537A (en) * | 1983-04-30 | 1984-11-15 | Yamatake Honeywell Co Ltd | Analog-digital communication device |
-
1985
- 1985-08-12 US US06/764,914 patent/US4816703A/en not_active Expired - Fee Related
-
1986
- 1986-04-30 IN IN341/CAL/86A patent/IN165456B/en unknown
- 1986-05-23 KR KR1019860004060A patent/KR870002507A/en not_active IP Right Cessation
- 1986-05-30 CA CA000510378A patent/CA1243095A/en not_active Expired
- 1986-06-25 ES ES556791A patent/ES8800458A1/en not_active Expired
- 1986-06-27 AU AU59421/86A patent/AU585032B2/en not_active Ceased
- 1986-07-14 BR BR8603294A patent/BR8603294A/en unknown
- 1986-08-01 DE DE8686305965T patent/DE3679119D1/en not_active Expired - Fee Related
- 1986-08-01 EP EP86305965A patent/EP0212897B1/en not_active Expired - Lifetime
- 1986-08-07 JP JP61184359A patent/JPS6239925A/en active Pending
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4166963A (en) * | 1976-09-30 | 1979-09-04 | The Solartron Electronic Group Limited | Buffer circuit for a data highway |
US4623799A (en) * | 1985-03-27 | 1986-11-18 | Trw Inc. | High speed analog/digital driver |
US4691328A (en) * | 1985-08-12 | 1987-09-01 | The Babcock & Wilcox Company | On-line serial communication interface from a computer to a current loop |
US4729125A (en) * | 1985-08-12 | 1988-03-01 | The Babcock & Wilcox Company | On-line serial communication interface to a transmitter from a current loop |
Non-Patent Citations (6)
Title |
---|
"Byte", p. 330, AD inquiry 26, McGraw Hill. |
"IC Schematic Source Master", John Wiley & Sons, 1978, p. 342, Precision Process Control Interface. |
"Understanding Data Communications", by G. E. Friend et al., 1984, Texas Instruments, pp. 4-25 to 4-26. |
Byte , p. 330, AD inquiry 26, McGraw Hill. * |
IC Schematic Source Master , John Wiley & Sons, 1978, p. 342, Precision Process Control Interface. * |
Understanding Data Communications , by G. E. Friend et al., 1984, Texas Instruments, pp. 4 25 to 4 26. * |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5451923A (en) * | 1992-10-05 | 1995-09-19 | Fisher Controls International, Inc. | Communication system and method |
US5684451A (en) * | 1992-10-05 | 1997-11-04 | Fisher Controls International, Inc. | Communication system and method |
US5694109A (en) * | 1996-09-04 | 1997-12-02 | International Controls And Measurement Corp. | Two-wire dc communication system and transceiver |
US9812825B2 (en) | 1998-04-10 | 2017-11-07 | Chrimar Systems, Inc. | Ethernet device |
US20030053547A1 (en) * | 2001-08-22 | 2003-03-20 | Peter Aberl | Serial interface unit with transmit monitor |
US7085325B2 (en) * | 2001-08-22 | 2006-08-01 | Texas Instruments Incorporated | Serial interface unit with transmit monitor |
Also Published As
Publication number | Publication date |
---|---|
EP0212897A2 (en) | 1987-03-04 |
EP0212897B1 (en) | 1991-05-08 |
ES556791A0 (en) | 1987-11-01 |
EP0212897A3 (en) | 1988-01-20 |
CA1243095A (en) | 1988-10-11 |
AU585032B2 (en) | 1989-06-08 |
BR8603294A (en) | 1987-03-17 |
KR870002507A (en) | 1987-03-31 |
IN165456B (en) | 1989-10-21 |
DE3679119D1 (en) | 1991-06-13 |
JPS6239925A (en) | 1987-02-20 |
AU5942186A (en) | 1987-02-19 |
ES8800458A1 (en) | 1987-11-01 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: BABCOCK & WILCOX COMPANY, THE, NEW ORLEANS, LA., A Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:STERLING, EDWARD L. JR.;THOMPSON, WILLIAM L.;REEL/FRAME:004446/0468 Effective date: 19850809 |
|
AS | Assignment |
Owner name: BABCOCK & WILCOX TRACY POWER, INC., A CORP. OF DE, Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:BABCOCK & WILCOX COMPANY, THE, A CORP. OF DE;REEL/FRAME:005161/0198 Effective date: 19890831 |
|
AS | Assignment |
Owner name: ELSAG INTERNATIONAL B.V., A CORP. OF THE NETHERLAN Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:BABCOCK & WILCOX TRACY POWER, INC., A CORP. OF DE;REEL/FRAME:005238/0432 Effective date: 19891031 |
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CC | Certificate of correction | ||
REMI | Maintenance fee reminder mailed | ||
LAPS | Lapse for failure to pay maintenance fees | ||
FP | Lapsed due to failure to pay maintenance fee |
Effective date: 19930328 |
|
STCH | Information on status: patent discontinuation |
Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362 |